Approach for enhancing emissions control device warmup in a direct injection engine system

ABSTRACT

A method of controlling fuel supplied to an engine of a vehicle is provided. The vehicle includes a first fuel storage tank to store a first type of fuel, a second fuel storage tank to store a second type of fuel, and an emissions control device. The engine includes at least one cylinder having a direct injection fuel injector being selectively supplied with the first type of fuel from the first fuel storage tank and the second type of fuel from the second fuel storage tank. The method includes supplying the first type of fuel from the first fuel storage tank to the direct injection fuel injector in response an engine start condition of the vehicle, and supplying the second type of fuel from the second fuel storage tank to the direct injection fuel injector, in response to an increase in engine output exceeding a threshold increase or a temperature of the emissions control device exceeding a threshold temperature.

BACKGROUND AND SUMMARY

An engine of a vehicle may include a cylinder having a direct injectionfuel injector and a port injection fuel injector. The port injectionfuel injector may be supplied with gasoline only from a first fuelstorage tank and the direct injection fuel injector may be supplied withethanol only from a second fuel storage tank. This engine configurationis one example of what may be referred to as an ethanol boosted systemwhich may be used to enhance engine operating efficiency and improvefuel economy performance. For example, under some conditions, the portinjection fuel injector may inject a reduced amount of gasoline and thedirect injection fuel injector may inject ethanol to abate engine knockwhich otherwise would be caused by operation at increased boost levelsand/or compression ratios.

The inventors herein have recognized issues with the above approach. Inparticular, in the above engine configuration, at cold engine startstart-up, an emissions control device of the vehicle may be at atemperature below an operational light-off temperature, and thus quickheating of the emissions control device may be desired to controlvehicle emissions. However, at a cold engine start-up condition, directinjection of ethanol for combustion may result in unstable combustion ormodest heat generation since ethanol may not vaporize at coldtemperatures. Likewise, port injected gasoline for combustion mayproduce modest heat generation resulting in slower emissions controldevice warm-up.

At least some of the above issues may be overcome, in one approach, by amethod of controlling fuel supplied to an engine of a vehicle, thevehicle including a first fuel storage tank to store a first type offuel, a second fuel storage tank to store a second type of fuel, and anemissions control device, the engine including at least one cylinderhaving a direct injection fuel injector being selectively supplied withthe first type of fuel from the first fuel storage tank and the secondtype of fuel from the second fuel storage tank, the method comprising:supplying the first type of fuel from the first fuel storage tank to thedirect injection fuel injector in response an engine start condition ofthe vehicle; and supplying the second type of fuel from the second fuelstorage tank to the direct injection fuel injector, in response to anincrease in engine output exceeding a threshold increase or atemperature of the emissions control device exceeding a thresholdtemperature.

In one example, gasoline is supplied to the direct injection fuelinjector at cold engine start-up and the direct injection fuel injectorperforms mild stratified injections of gasoline. In particular, atengine startup, gasoline may be preferable for direct injection overethanol because gasoline vaporizes at cooler temperatures relative toethanol. The vaporized gasoline may form a stratified mixture of air andfuel providing enhanced combustion stability that enables additionalspark retard for increased exhaust heat. Thus, by supplying stratifiedgasoline via the direct injector at engine startup exhaust heatgeneration may be increased. In this way, an emissions control devicemay be heated to a light-off temperature in a quick manner.

Furthermore, upon the emissions control device reaching the light-offtemperature, gasoline is no longer needed for heating of the emissionscontrol device, thus ethanol is supplied to the direct injection fuelinjector. Also, if the engine load increases to a substantially highload prior to the emissions control device reaching the light-offtemperature, ethanol may be supplied to the direct injection fuelinjector for knock suppression purposes. In particular, the directlyinjected ethanol may provide substantial charge cooling due to thehigher heat of vaporization of ethanol resulting in suppression ofengine knock. By suppressing engine knock, engine output may beincreased without substantial engine degradation. In this way, theoperating efficiency of the engine may be improved.

Accordingly, the above described approach may supply gasoline to thedirect injection fuel injectors for improved emissions control deviceheating at engine startup. Then, the approach may transition tosupplying ethanol to the direct injection fuel injectors to suppressengine knock and increase output. In this way, the vehicle emission maybe reduced and operating efficiency may be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of engine system of thepresent disclosure.

FIG. 2 a is a schematic view of an embodiment of a fuel system inoperative communication with an engine system of the present disclosure.

FIG. 2 b is a schematic view of another embodiment of a fuel system ofthe present disclosure.

FIG. 2 c is a schematic view of yet another embodiment of a fuel systemof the present disclosure.

FIG. 3 is a flowchart of an embodiment of a method of improving exhaustsystem warm-up by supplying different types of fuel, under differentoperating conditions, to direct injection fuel injectors of an enginesystem, for enhanced operation of the engine system.

FIG. 4 is a flowchart of another embodiment of a method of providingdifferent types of fuel, under different operating conditions, to directinjection fuel injectors of an engine system, for enhanced operation ofthe engine system.

FIG. 5 is a flowchart of an embodiment of a method of reducing thelikelihood of overheating of direct injection fuel injectors of anengine system by switching the source from which fuel is supplied to thedirect injection fuel injectors.

DETAILED DESCRIPTION

FIG. 1 shows one cylinder of a multi-cylinder engine, as well as theintake and exhaust path connected to that cylinder. In the embodimentshown in FIG. 1, engine 10 is capable of using two different fuels,and/or two different injectors in one example. For example, engine 10may use gasoline and an alcohol containing fuel such as ethanol,methanol, a mixture of gasoline and ethanol (e.g., E85 which isapproximately 85% ethanol and 15% gasoline), a mixture of gasoline andmethanol (e.g., M85 which is approximately 85% methanol and 15%gasoline), etc. In another example, two fuel systems are used, but eachuses the same fuel, such as gasoline. In still another embodiment, asingle injector (such as a direct injector) may be used to inject amixture of gasoline and an alcohol based fuel, where the ratio of thetwo fuel quantities in the mixture may be adjusted by controller 12 viaa mixing valve, for example. In still another example, two differentinjectors for each cylinder are used, such as port injection (PI) fuelinjectors and direct injection (DI) fuel injectors. In even anotherembodiment, different sized injectors, in addition to differentlocations and different fuels, may be used.

As will be described in more detail below, various advantageous resultsmay be obtained by variations of the above systems. For example, whenusing both gasoline and a fuel having alcohol (e.g., ethanol), it may bepossible to adjust the relative amounts of the fuels to take advantageof the increased charge cooling of alcohol fuels (e.g., via directinjection) to reduce the tendency of knock. This phenomenon, combinedwith increased compression ratio, and/or boosting and/or enginedownsizing, can then be used to obtain large fuel economy benefits (byreducing the knock limitations on the engine).

FIG. 1 shows one example fuel system with two fuel injectors percylinder, for at least one cylinder. Further, each cylinder may have twofuel injectors. The two injectors may be configured in variouslocations, such as two port injectors, two direct injectors, one portinjector and one direct injector (as shown in FIG. 1), or others.

Continuing with FIG. 1, it shows a dual injection system, where engine10 has both direct and port fuel injection, as well as spark ignition.Internal combustion engine 10, comprising a plurality of combustionchambers, is controlled by electronic engine controller 12. Combustionchamber 30 of engine 10 is shown including combustion chamber walls 32with piston 36 positioned therein and connected to crankshaft 40. Astarter motor (not shown) may be coupled to crankshaft 40 via a flywheel(not shown), or alternatively direct engine starting may be used.

In one particular example, piston 36 may include a recess or bowl (notshown) to help in forming stratified charges of air and fuel, ifdesired. However, in an alternative embodiment, a flat piston may beused.

Combustion chamber, or cylinder, 30 is shown communicating with intakemanifold 44 and exhaust manifold 48 via respective intake valve 52 a,and exhaust valve 54 a. Thus, while two valves per cylinder may be used,in another example, four valves per cylinder may be used. That is, twointake valves and two exhaust valves per cylinder may be used. In stillanother example, two intake valves and one exhaust valve per cylindermay be used.

Combustion chamber 30 can have a compression ratio, which is the ratioof volumes when piston 36 is at bottom center to top center. In oneexample, the compression ratio may be approximately 9:1. However, insome examples where different fuels are used, the compression ratio maybe increased. For example, it may be between 10:1 and 11:1 or 11:1 and12:1, or greater.

Fuel injector 66A is shown directly coupled to combustion chamber 30 fordelivering injected fuel directly therein in proportion to the pulsewidth of signal dfpw received from controller 12 via electronic driver68. While FIG. 1 shows injector 66A as a side injector, in someembodiment the injector may be located overhead of the piston, such asnear the position of spark plug 92. Such a position may improve mixingand combustion due to the lower volatility of some alcohol based fuels,and further may improve mixing and combustion of gasoline based fuelthat is directly injected into the cylinder. Alternatively, the injectormay be located overhead and near the intake valve to improve mixing.

Fuel injector 66B is shown coupled to intake manifold 44, rather thandirectly to cylinder 30. Fuel injector 66B delivers injected fuel inproportion to the pulse width of signal pfpw received from controller 12via electronic driver 68. Note that a single driver 68 may be used forboth fuel injection systems, or multiple drivers may be used. Fuelsystem 164 is also shown in schematic form delivering vapors to intakemanifold 44. Various fuel systems and fuel vapor purge systems may beused as well as EGR systems to improve vehicle operating efficiency.

Intake manifold 44 is shown communicating with throttle body 58 viathrottle plate 62. In this particular example, throttle plate 62 iscoupled to electric motor 94 so that the position of elliptical throttleplate 62 is controlled by controller 12 via electric motor 94. Thisconfiguration may be referred to as electronic throttle control (ETC),which can also be utilized during idle speed control.

Exhaust gas sensor 76 is shown coupled to exhaust manifold 48 upstreamof catalytic converter 70 (where sensor 76 can correspond to variousdifferent sensors). For example, sensor 76 may be any of many knownsensors for providing an indication of exhaust gas air/fuel ratio suchas a linear oxygen sensor, a UEGO, a two-state oxygen sensor, an EGO, aHEGO, or an HC or CO sensor. In this particular example, sensor 76 is atwo-state oxygen sensor that provides signal EGO to controller 12 whichconverts signal EGO into two-state signal EGOS. A high voltage state ofsignal EGOS indicates exhaust gases are rich of stoichiometry and a lowvoltage state of signal EGOS indicates exhaust gases are lean ofstoichiometry. Signal EGOS may be used to advantage during feedbackair/fuel control to maintain average air/fuel at stoichiometry during astoichiometric homogeneous mode of operation or during stoichiometricstratified mode of operation.

Distributorless ignition system 88 provides ignition spark to combustionchamber 30 via spark plug 92 in response to spark advance signal SA fromcontroller 12.

Controller 12 may cause combustion chamber 30 to operate in a variety ofcombustion modes, including a homogeneous air/fuel mode and a stratifiedair/fuel mode by controlling injection timing, injection amounts, spraypatterns, etc. Further, combined stratified and homogenous mixtures maybe formed in the chamber. In one example, stratified layers may beformed by operating injector 66A during a compression stroke. In anotherexample, a homogenous mixture may be formed by operating one or both ofinjectors 66A and 66B during an intake stroke (which may be open valveinjection). In yet another example, a homogenous mixture may be formedby operating one or both of injectors 66A and 66B before an intakestroke (which may be closed valve injection). In still other examples,multiple injections from one or both of injectors 66A and 66B may beused during one or more strokes (e.g., intake, compression, exhaust,etc.). Even further examples may be where different injection timingsand mixture formations are used under different conditions, as describedbelow.

Controller 12 can control the amount of fuel delivered by fuel injectors66A and 66B so that the homogeneous, stratified, or combinedhomogenous/stratified air/fuel mixture in chamber 30 can be selected tobe at stoichiometry, a value rich of stoichiometry, or a value lean ofstoichiometry.

Emission control device 72 is shown positioned downstream of catalyticconverter 70. Emission control device 72 may be a three-way catalyst ora NOx trap, or combinations thereof.

Controller 12 is shown as a microcomputer, including microprocessor unit102, input/output ports 104, an electronic storage medium for executableprograms and calibration values shown as read only memory chip 106 inthis particular example, random access memory 108, keep alive memory110, and a conventional data bus. Controller 12 is shown receivingvarious signals from sensors coupled to engine 10, in addition to thosesignals previously discussed, including measurement of inducted mass airflow (MAF) from mass air flow sensor 100 coupled to throttle body 58;engine coolant temperature (ECT) from temperature sensor 112 coupled tocooling sleeve 114; a profile ignition pickup signal (PIP) from Halleffect sensor 118 coupled to crankshaft 40; and throttle position TPfrom throttle position sensor 120; absolute Manifold Pressure Signal MAPfrom sensor 122; an indication of knock from knock sensor 182; and anindication of absolute or relative ambient humidity from sensor 180.Engine speed signal RPM is generated by controller 12 from signal PIP ina conventional manner and manifold pressure signal MAP from a manifoldpressure sensor provides an indication of vacuum, or pressure, in theintake manifold. During stoichiometric operation, this sensor can givean indication of engine load. Further, this sensor, along with enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, produces a predetermined number of equally spacedpulses every revolution of the crankshaft.

In this particular example, temperature Tcat1 of catalytic converter 70is provided by temperature sensor 124 and temperature Tcat2 of emissioncontrol device 72 is provided by temperature sensor 126. In an alternateembodiment, temperature Tcat1 and temperature Tcat2 may be inferred fromengine operation.

Further, as shown in FIG. 2, controller 12 may receive signals from fuelsensor 238 and fuel sensor 240. The signals from fuel sensor 238 mayprovide an indication of an amount or level of fuel in first fuelstorage tank 230 and the signals from fuel sensor 240 may provide andindication of an amount or level of fuel in second fuel storage tank234.

Returning to FIG. 1, a variable camshaft timing system is shown.Specifically, camshaft 130 of engine 10 is shown communicating withrocker arms 132 and 134 for actuating intake valves 52 a, 52 b andexhaust valves 54 a, 54 b. Camshaft 130 is directly coupled to housing136. Housing 136 forms a toothed wheel having a plurality of teeth 138.Housing 136 is hydraulically coupled to crankshaft 40 via a timing chainor belt (not shown). Therefore, housing 136 and camshaft 130 rotate at aspeed substantially equivalent to the crankshaft. However, bymanipulation of the hydraulic coupling, the relative position ofcamshaft 130 to crankshaft 40 can be varied by hydraulic pressures inadvance chamber 142 and retard chamber 144. By allowing high pressurehydraulic fluid to enter advance chamber 142, the relative relationshipbetween camshaft 130 and crankshaft 40 is advanced. Thus, intake valve52 a and exhaust valve 54 a open and close at a time earlier than normalrelative to crankshaft 40. Similarly, by allowing high pressurehydraulic fluid to enter retard chamber 144, the relative relationshipbetween camshaft 130 and crankshaft 40 is retarded. Thus, intake valve52 a and exhaust valve 54 a open and close at a time later than normalrelative to crankshaft 40.

While this example shows a system in which the intake and exhaust valvetiming are controlled concurrently, variable intake cam timing, variableexhaust cam timing, dual independent variable cam timing, or fixed camtiming may be used. Further, variable valve lift may also be used.Further, camshaft profile switching may be used to provide different camprofiles under different operating conditions. Further still, thevalvetrain may include a roller finger follower, direct actingmechanical bucket, electromechanical, electrohydraulic, or otheralternatives to rocker arms.

Continuing with the variable cam timing system, teeth 138, being coupledto housing 136 and camshaft 130, allow for measurement of relative camposition via cam timing sensor 150 providing signal VCT to controller12. Teeth 1, 2, 3, and 4 are preferably used for measurement of camtiming and are equally spaced (for example, in a V-8 dual bank engine,spaced 90 degrees apart from one another) while tooth 5 is preferablyused for cylinder identification. In addition, controller 12 sendscontrol signals (LACT, RACT) to conventional solenoid valves (not shown)to control the flow of hydraulic fluid either into advance chamber 142,retard chamber 144, or neither.

Relative cam timing can be measured in a variety of ways. In generalterms, the time, or rotation angle, between the rising edge of the PIPsignal and receiving a signal from one of the plurality of teeth 138 onhousing 136 gives a measure of the relative cam timing. For theparticular example of a V-8 engine, with two cylinder banks and afive-toothed wheel, a measure of cam timing for a particular bank isreceived four times per revolution, with the extra signal used forcylinder identification.

Sensor 160 may also provide an indication of oxygen concentration in theexhaust gas via signal 162, which provides controller 12 a voltageindicative of the O2 concentration. For example, sensor 160 can be aHEGO, UEGO, EGO, or other type of exhaust gas sensor. Also note that, asdescribed above with regard to sensor 76, sensor 160 can correspond tovarious different sensors.

As described above, FIG. 1 merely shows one cylinder of a multi-cylinderengine, and that each cylinder has its own set of intake/exhaust valves,fuel injectors, spark plugs, etc.

Also, in the example embodiments described herein, the engine may becoupled to a starter motor (not shown) for starting the engine. Thestarter motor may be powered when the driver turns a key in the ignitionswitch on the steering column, for example. The starter is disengagedafter engine starting, for example, by engine 10 reaching apredetermined speed after a predetermined time. Further, in thedisclosed embodiments, an exhaust gas recirculation (EGR) system may beused to route a desired portion of exhaust gas from exhaust manifold 48to intake manifold 44 via an EGR valve (not shown). Alternatively, aportion of combustion gases may be retained in the combustion chambersby controlling exhaust valve timing.

As noted above, engine 10 may operate in various modes, including leanoperation, rich operation, and “near stoichiometric” operation. “Nearstoichiometric” operation can refer to oscillatory operation around thestoichiometric air fuel ratio. Typically, this oscillatory operation isgoverned by feedback from exhaust gas oxygen sensors. In this nearstoichiometric operating mode, the engine may be operated withinapproximately one air-fuel ratio of the stoichiometric air-fuel ratio.This oscillatory operation is typically on the order of 1 Hz, but canvary faster and slower than 1 Hz. Further, the amplitude of theoscillations are typically within 1 a/f ratio of stoichiometry, but canbe greater than 1 a/f ratio under various operating conditions. Notethat this oscillation does not have to be symmetrical in amplitude ortime. Further note that an air-fuel bias can be included in theoperation, where the bias is adjusted slightly lean, or rich, ofstoichiometry (e.g., within 1 a/f ratio of stoichiometry). Also notethat this bias and the lean and rich oscillations can be governed by anestimate of the amount of oxygen stored in upstream and/or downstreamthree way catalysts.

As another example, the engine may operate in stratified fuel injectionmode. In stratified fuel injection mode, the DI fuel injectors and/orthe PI, combined or alone, may perform separate injection events duringthe intake stroke (for a homogeneous mixture which is approximatelystoichiometric) and late in the compression stroke (to add extra fuelnear the spark plug). The injections create locally rich mixture nearthe spark plug that improves combustion stability.

Feedback air-fuel ratio control may be used for providing the nearstoichiometric operation. Further, feedback from exhaust gas oxygensensors can be used for controlling air-fuel ratio during lean andduring rich operation. In particular, a switching type, heated exhaustgas oxygen sensor (HEGO) can be used for stoichiometric air-fuel ratiocontrol by controlling fuel injected (or additional air via throttle orVCT) based on feedback from the HEGO sensor and the desired air-fuelratio. Further, a UEGO sensor (which provides a substantially linearoutput versus exhaust air-fuel ratio) can be used for controllingair-fuel ratio during lean, rich, and stoichiometric operation. In thiscase, fuel injection (or additional air via throttle or VCT) can beadjusted based on a desired air-fuel ratio and the air-fuel ratio fromthe sensor. Further still, individual cylinder air-fuel ratio controlcould be used, if desired. As described in more detail below,adjustments may be made with injector 66A, 66B, or combinationstherefore depending on various factors.

Also note that various methods can be used to maintain the desiredtorque such as, for example, adjusting ignition timing, throttleposition, variable cam timing position, exhaust gas recirculationamount, and number of cylinders carrying out combustion. Further, thesevariables can be individually adjusted for each cylinder to maintaincylinder balance among all the cylinders.

Referring now to FIG. 2 a, an example engine 10 with four in-linecylinders and a corresponding fuel system 20 is shown. In oneembodiment, engine 10 may have a turbocharger 219, which has a turbine219 a coupled in exhaust manifold 48 and a compressor 219 b coupled inintake manifold 44. While FIG. 2 a does not show an intercooler, one mayoptionally be used. Turbine 219 a is typically coupled to compressor 219b via a drive shaft 215. Various types of turbochargers and arrangementsmay be used. For example, a variable geometry turbocharger (VGT) may beused where the geometry of the turbine and/or compressor may be variedduring engine operation by controller 12. Alternately, or in addition, avariable nozzle turbocharger (VNT) may be used when a variable areanozzle is placed upstream and/or downstream of the turbine in theexhaust line (and/or upstream or downstream of the compressor in theintake line) for varying the effective expansion or compression ofgasses through the turbocharger. Still other approaches may be used forvarying expansion in the exhaust, such as a waste gate valve. FIG. 2 ashows an example bypass valve 220 around turbine 219 a and an examplebypass valve 222 around compressor 219 b, where each valve may becontrolled via controller 12. As noted above, the valves may be locatedwithin the turbine or compressor, or may be a variable nozzle.

Also, a twin turbocharger arrangement, and/or a sequential turbochargerarrangement, may be used if desired. In the case of multiple adjustableturbocharger and/or stages, it may be desirable to vary a relativeamount of expansion though the turbocharger, depending on operatingconditions (e.g. manifold pressure, airflow, engine speed, etc.).Further, a supercharger may be used, if desired.

Fuel system 20 may deliver one or more different types of fuel to engine10 via port injection (PI) fuel injectors 66B and/or direct injection(DI) fuel injectors 66A. The different fuel types may include fuels withdifferent octanes, different heats of vaporization, differentconcentrations of a gasoline/alcohol mixture, combinations thereof, etc.In one example, the first type of fuel may include a 10% ethanol blendin gasoline, while in another example, the second type of fuel mayinclude an 85% ethanol blend in gasoline. However, still other differenttypes of fuel may be used.

In the illustrated embodiment, an example fuel system configuration isshown where a separate fuel pump and tank is provided for a first andsecond fuel type. Specifically, a first tank 230 is shown for holdingliquid fuel of a first type. First tank 230 may receive the first fueltype via filler tube 232. Likewise, a second tank 234 to hold liquidfuel of a second type may receive the second fuel type via filler tube236. In one example, the first tank contains gasoline, while the secondtank contains an alcohol blend, such as ethanol or an ethanol-gasolinemixture. However, other fuel types may also be used. It will beappreciated that in some cases both the first and second fuel storagetanks may hold the same type of liquid fuel.

The liquid fuel level in fuel storage tanks 230 and 234 may bedetermined by controller 12 using sensor measurements. For example,sensor 238 may measure the fuel storage tank pressure of fuel storagetank 230 and a liquid fuel level of the first type of fuel may bederived from that pressure measurement. Likewise, sensor 240 may measurethe fuel storage tank pressure of fuel storage tank 234 and a liquidfuel level of the second type of fuel may be derived from that pressuremeasurement. As another example, in some embodiments, a liquid fuellevel measuring device (not shown) that floats on the surface of theliquid fuel in the tank may determine the volume of liquid fuel in thetank. It will be appreciated that an indication of the liquid fuel levelmay be provided to the driver based on a determination via measurement,calculation, or combination thereof. Controller 12 may generate a fuellevel reading that may range between a full fuel storage tank and anempty fuel storage tank based on the received measurements and/or thedetermination. The indication may be displayed to the vehicle operatorvia a fuel level indicator (not shown) that may be used by the vehicleoperator for fuel storage tank filling purposes.

Fuel system 20 further includes fuel vapor canister 264 that connects tofuel storage tanks 230 and 234 via vent pipe 262. Fuel vapor canister264 may trap fuel vapor flowing into the canister while allowing airfiltered through the canister to be vented to the atmosphere via an airvent (not shown). In some embodiments, the fuel vapor canister mayfilter fuel vapor with charcoal. The fuel vapor may adhere to thecharcoal until the fuel vapor is purged.

Fuel vapor canister saturation may occur responsive to various operatingconditions and events. In one example, fuel storage tank filling mayforce fuel vapor residing in the fuel storage tank into the canistercausing canister saturation. As another example, heat and/or pressuregenerated during vehicle operation may cause liquid fuel to evaporatecreating fuel vapor which may be transferred into the canister causingsaturation.

In order to avoid over saturation of fuel vapor canister 264 and releaseof fuel vapor to the atmosphere, fuel vapor may be purged from fuelvapor canister 264 via purge valve 266 which may be actuated bycontroller 12. Fuel vapor may be purged from the fuel vapor canisterusing engine vacuum created during engine operation. In one example,engine vacuum may be created by actuating throttle valve 62 and uponactuation of purge valve 266; fuel vapor may travel from fuel vaporcanister 264 into the intake manifold and enter cylinders of engine 10for combustion. By introducing fuel vapor into the cylinder and not intothe atmosphere fuel economy may be improved and emissions may bereduced. In some configurations, each fuel storage tank may have aseparate vapor passage in communication with a shared fuel vaporcanister. Further, in some configurations each fuel storage tank mayhave a separate fuel vapor passage in communication with a separate fuelvapor canister.

A first type of liquid fuel (e.g. gasoline) may be pumped from fuelstorage tank 230 into passage 246 via pump 242. Passage 246 may lead toPI injector 66B via fuel rail 248 for port injection of the first fueltype to cylinders of engine 10 in what may be referred to as the portinjection system. Further, passage 246 may lead to valve 256. In someembodiments, valve 256 is a solenoid valve. A second type of liquid fuel(e.g. ethanol, ethanol/gasoline) may be pumped from fuel storage tank234 into passage 252 via low pressure pump 250. Passage 252 may lead tovalve 256. Valve 256 may be actuated by controller 12 to selectivelysupply the first fuel type from fuel storage tank 230 or the second fueltype from fuel storage tank 234 to high pressure pump 258 which mayprovide fuel to DI fuel injector 66A via fuel rail 260 for directinjection of the first or second fuel to cylinders of engine 10 whichmay be referred to as the DI system. By selectively supplying each ofthe different fuel types to the DI fuel injectors, different combustionmodes may be performed throughout engine operation that take advantageof the properties of the different types of fuel. For example, gasolinemay be directly injected in a stratified combustion mode during enginestartup in order to quickly warm up an emissions control device. Asanother example, ethanol may be directly injected during high engineloads to prevent engine knock. In this way, operating efficiency may beimproved and emissions may be reduced over the range of engineoperation.

Furthermore, by providing each of the different fuel types to the DIfuel injectors, liquid fuel may be provided to the DI fuel injectorseven when one of the fuel storage tanks is substantially empty. In thisway, degradation of the DI fuel injectors as a result of overheating maybe reduced or prevented since the DI fuel injectors may be cooled byfuel flowing through the injectors. Further still, by diverting thefirst type of fuel (e.g. gasoline) to the DI fuel injectors when thereis substantially none of the second type of fuel (e.g. ethanol,ethanol/gasoline), the engine may operate in a gasoline direct injectionoperating mode which may have improved efficiency over gasoline portinjection operation, under some conditions. Fuel injection controlstrategies will be discussed in further detail below with reference toFIGS. 3-5

While low pressure pumps 242 and 250 are shown outside the respectivefuel storage tanks, in an alternative example one or both of the pumpsmay be located within the respective fuel storage tanks. Further, thefuel systems may have different characteristics, such as different sizetanks, different size pumps, different pump capacity, different pumppressure, different pump maximum flows, different on/off cycles (e.g.,pump 250 may run more intermittently than pump 242), etc. Note, in someexamples, only one pump may operate under some conditions. For example,if fuel from tank 234 is not needed, or not enabled (e.g., during coldstart conditions), pump 250 may be deactivated (or not activated) whilepump 242 operates. In this way, less battery power may be used, and lessfuel vapors may be generated.

In some embodiments, the fuel system may include passages from both thefirst and second fuel storage tanks that may be used to selectivelysupply fuel to the PI fuel injectors via actuation of one or morevalves. In such a configuration, different types of fuel may be suppliedto the PI fuel injectors. In some embodiments, the fuel system mayinclude passages connecting the first fuel storage tank and the secondfuel storage tank to enable fuel to be transferred between the first andsecond fuel storage tanks. For example, if the second fuel storage tankis empty, gasoline in the first fuel storage tank may be pumped into thesecond fuel storage tank. Optionally (or alternatively), fuel may betransferred between various regions of the fuel system via gravity.

In some embodiments of fuel system 20, each fuel storage tank mayinclude separate fuel delivery and return lines controlled by differentvalves. As shown in FIG. 2 b, fuel system 20 may include first fuelstorage tank 230 in communication with passage 246 leading to valve 272and second fuel storage tank 234 in communication with passage 268leading to valve 270. Actuation of valves 270 and 272 may controldelivery of fuel from the respective fuel storage tanks to high pressurepump 258 and the DI system.

Further, fuel system 20 may include fuel return passage 278 incommunication with first fuel storage tank 230 and fuel return passage280 in communication with second fuel storage tank 234. Fuel may bepurged from the DI system via actuation of valves 274 and 276.Specifically, actuation of valve 274 may purge fuel into second fuelstorage tank 234 and actuation of valve 272 may purge fuel into firstfuel storage tank 230. It will be appreciated that in some embodimentsfuel may be purged via the high pressure fuel pump or another pump ofthe fuel system. In some embodiments, fuel may be transferred viagravity. By including selectively controlled return lines to each of thefuel storage tanks, the direct injection fuel system may be purgedwithout having to inject fuel into the cylinder and each of the fueltypes may be returned to their designated tanks with reduced mixing ofthe fuel types. In this way, fuel economy performance may be improved.

In some embodiments, the fuel system may include, for the fuel storagetanks, a returnless-type fuel system, a return-type fuel system, orcombinations thereof.

In some embodiments, fuel system 20 may be configured to receive ablended liquid fuel and substantially separate two or more differenttypes of liquid fuels from the blended liquid fuel into the fuel storagetanks. As shown in FIG. 2 c, fuel system may receive a blended liquidfuel (e.g., E85) via filling tube 290. The fuel may be separated byseparator 284 and a first fuel type may be supplied to first fuelstorage tank 230 via passage 288 and a second fuel type maybe suppliedto second fuel storage tank 234 via passage 286. In one example, E85 issupplied to the fuel system and the fuel separator separates gasolineand ethanol from an E85 blend and the gasoline is supplied to the firstfuel storage tank and the ethanol is supplied to the second fuel storagetank.

Further, the fuel system may include a single return passage 282 andcorresponding valve 280 that are configured to purge fuel from the DIsystem to fuel separator 284. The fuel separator may separate the purgedfuel into the appropriate fuel storage tank.

In some embodiments, the fuel separator may be positioned at the exit ofa fuel storage tank storing a blended fuel and the separator mayseparate the blended fuel into different types of fuel.

In some embodiments, the fuel system may include a primary fuel storagetank with a fuel separation layer and different types of fuels may beseparated into different regions of the primary fuel storage tank. Insuch a configuration, fuel purged from the DI system maybe returned tothe primary fuel storage tank.

It will be appreciated that various fuel supply regulating componentsdiscussed above may be included in a fuel supply control device. In oneexample, one or more of the fuel pumps and valves regulating flow in thefuel supply passages may be included in the fuel supply control device.

As discussed above, the engine system may operate in a variety ofdifferent combustion modes due, in part, to the use of multiple fuelinjectors to inject different types of fuel into cylinders of the enginevia direct injection and/or port injection. Furthermore, the ability ofthe fuel delivery system to selectively supply different types of fuelto the DI fuel injectors, under varying conditions, may be used toadvantage. In one example, the versatility of the fuel delivery systemmay be used to reduce the amount of time to warm-up emission controldevice(s) of a vehicle upon startup. Strategies for improved emissioncontrol device warm-up will be discussed in further detail herein withreference to FIGS. 3 and 4.

FIG. 3 shows a flowchart depicting an example fuel control strategy forimproved exhaust system warm-up at vehicle startup and improvedefficiency of engine operation across the operating range of the engine.In one example, the method may be applied to an engine system configuredto supply different types of fuel to DI fuel injectors. In someexamples, the engine may include a compression device such as aturbocharger, for example. Further, cylinders of the engine system mayinclude multiple fuel injectors and at least one of the fuel injectorsmay be selectively supplied with different types of fuel, such as theengine system configurations shown in FIGS. 1 and 2. More particularly,in this example, the engine system may be configured to inject a firsttype of fuel (e.g. gasoline) from a first fuel storage tank via PI fuelinjectors and at least some of either the first type of fuel (e.g.gasoline) or a second type of fuel (e.g. ethanol) from a second fuelstorage tank may be selectively supplied to DI fuel injectors for directinjection into cylinders of the engine.

It will be appreciated that the example method may be applied to othersuitable engine system configurations. For example, the method may beapplied to an engine system configuration that includes a fuel separatorto separate fuel to different fuel storage tanks. As another example,the PI fuel injectors may be omitted and the engine may only include oneor more DI fuel injectors per cylinder. Further, it will be appreciatedthe first and second fuel types may be any suitable types of fuel orfuel blends.

The flowchart begins at 302, where the method may include detecting akey-on condition. In other words, the method may include detecting adriver commanded vehicle/engine startup. If the key-on condition is notdetected the method may continue polling for the key-on condition.Otherwise, if the key-on condition is detected the flowchart moves to304.

At vehicle startup, the temperature of emissions control device(s) inthe vehicle's exhaust system may be below an operating or light-offtemperature. Thus, it may be desirable to heat the emissions controldevice(s) in a quick manner in order to reduce tailpipe emissions.Therefore, at 304, the method may include performing stratified fuelinjections of gasoline via the DI fuel injectors. Gasoline may beprovided to the DI fuel injectors from a first fuel storage tank. Mildstratification may be enabled by direct injection, using separateinjection events during an intake stroke (for a homogeneous mixturewhich is approximately stoichiometric) and late in the compressionstroke (to add extra fuel near the spark plug). In particular, thestratified injection(s) may result in a locally rich mixture near thespark plug that improves combustion stability, and therefore enablesadditional spark retard for increased exhaust heat that may betransferred to emission control devise(s) for improved warm-up. It willbe appreciated that, under some conditions, at vehicle start-up,gasoline may be supplied to the DI fuel injectors and the PI fuelinjectors. Moreover, gasoline may be directly injected at startup,because gasoline may vaporize at a lower temperature relative to ethanolresulting in greater combustion stability.

Performing stratified injections of gasoline (or another fuel type thatvaporizes in cold conditions) to quickly heat the exhaust system may beparticularly beneficial in turbocharged engine applications because theadded mass and surface area of a turbocharger may reduce the heatavailable at the catalyst emission control devise(s) for warm-uppurposes.

Next at 306, the method may include detecting if a tip-in of theaccelerator pedal or other increase in engine output has occurred. Insome examples, the increase in engine output may be commanded to producehigh output or high engine load. In some examples, tip-in may bedetected based on a change in pedal position exceeding a thresholdchange (or pedal position). If a sufficient tip-in of the acceleratorpedal is detected the flowchart moves to 312. Otherwise, the flowchartmoves to 308.

Next at 308, the method may include determining if the temperature ofthe emissions control device(s) (ECD) is greater than a thresholdlight-off temperature. The threshold light-off temperature may include atemperature at which an emissions control device suitably reduces theless desirable emissions exhausted from cylinders of the engine. If itis determined that the emissions control device(s) has/have not reachedthe threshold light-off temperature, the flowchart returns to 304 andstratified injections of gasoline may be performed to continue warm-upof the emissions control device(s). Otherwise, if it is determined thatthe emissions control device(s) has/have reached the threshold light-offtemperature, and the flowchart moves to 310.

Optionally (or alternatively), in some embodiments, it may be determinedif a temperature of the cylinder has reached a threshold temperature. Inone example, the threshold temperature is the temperature at whichethanol vaporizes well enough to achieve a desired combustion stabilitylevel. Temperature in a cylinder can be estimated by counting the numberof combustion events and the air charge temperature. An empiricallydetermined table that is indexed by the number of combustion events in aparticular cylinder and air charge temperature is one way to estimatetemperature in a cylinder. When the estimated cylinder temperaturereaches the predetermined level the second fuel is delivered to thecylinder's direct injector.

Furthermore, in some embodiments, upon reaching a cylinder temperatureat which ethanol may be stably combusted, the DI fuel injector maytransition from using gasoline from the first fuel storage tank toinjecting stratified ethanol from the second fuel storage tank byincreasing the ethanol fraction (EF). In this way, the combustionbenefits of stratified ethanol may be applied to the temperature rangebetween stable combustion of ethanol and warm-up of the emissionscontrol device. Note that injections of stratified ethanol from thesecond storage tank may be performed at an engine start where thecylinder temperature reaches the predetermined level.

At 310, the method may include performing homogeneous fuel injections ofgasoline from the first fuel storage tank via the DI fuel injectors.Since the emissions control device has reached a light-off temperature,additional heat does need not be generated from direct injection ofstratified gasoline and homogeneous operation may be performed.

Turning to 312, the method may include supplying ethanol to the DI fuelinjectors from the second fuel storage tank. In one example, ethanol maybe supplied to the DI system in response to detection of a commandedhigh engine load condition, so that ethanol may be directly injected toabate engine knock during the high engine load condition. In particular,ethanol has a higher heat of vaporization relative to gasoline, soethanol directly injected into the combustion chamber may provideincreased air charge cooling to abate engine knock and allowing for anincrease in the amount of boost resulting in increased engine output. Itwill be appreciated that gasoline from the first fuel storage tank maynot be supplied to the DI system when ethanol from the second fuelstorage tank is supplied to the DI system, such as at accelerator pedaltip-in, for example.

It will be appreciated that supplying fuel (e.g. ethanol or gasoline) tothe DI fuel injectors may include actuation of one or more valves in thefuel system to stop the flow of the first fuel type and start the flowof the second fuel type. In some embodiments, the fuel system mayinclude separate supply lines with separate valves to the DI system andeach of the valves may be actuated to supply the appropriate fuel typeto the DI system. In some embodiments, a single valve may selectivelycontrol which fuel type is supplied to the DI system.

Next at 314, the method may include adjusting the fuel injection amountinjected by the DI fuel injectors and/or the PI fuel injectors. Forexample, the amount of fuel injected by the DI fuel injectors may beincreased in order to quickly purge the DI system of gasoline.Cooperatively, the amount of fuel injected via the PI fuel injectors maybe reduced as the amount of fuel injected via the DI fuel injectors isincreased in order to maintain a desired air/fuel ratio. In someexamples, the desired air/fuel ratio may include stoichiometric air/fuelratio.

Under some conditions, the amount of fuel injected via the DI fuelinjectors may be initially increased to purge the DI system and thenreduced to another desired level once the gasoline has been purged fromthe DI system. In some examples, the adjusted fuel amount may beinjected for a predetermined duration. In some examples, the adjustedfuel amount may be injected for a duration based on a model of the fuelsystem volume and fuel flow rates in and out of the system. Under someconditions, the amount of fuel injected via the DI fuel injectors may beinitially increased to purge the DI system and may be maintained at thatamount to avoid knock. In one particular example, where gasoline andethanol may be selectively supplied to the DI system, the method mayincrease the desired ethanol fraction (EF) during a tip-in, until the DIsystem is purged of gasoline.

Next at 316, the method may include detecting a tip-out of theaccelerator pedal or other decrease in engine output. In one example,the decrease in engine output may be commanded to low output or lowengine load. In one example, tip-out is detected based on a change inpedal position exceeding a threshold change (or pedal position). If atip-out to lower load is detected the flowchart moves to 318. Otherwise,the flowchart returns to 316 and polls for a tip-out of the acceleratorpedal.

At 318, the method may include supplying gasoline from the first fuelstorage tank to the DI fuel injectors. Gasoline may be provided to theDI system at tip-out and ethanol may be purged from the DI system inpreparation for engine shutdown and an ensuing engine restart. Asdiscussed above, at a cold start condition, stratified gasoline may bedirectly injected to speed up emissions control device warm-up, sincegasoline has a lower evaporation temperature than ethanol and thus mayimprove combustion stability at lower temperatures relative to ethanol.It will be appreciated that ethanol from the second fuel storage tankmay not be supplied to the DI system when gasoline from the first fuelstorage tank is supplied to the DI system, such as at accelerator pedaltip-out, for example.

Next at 320, the method may include adjusting the fuel injection amountinjected by the DI fuel injectors and/or the PI fuel injectors. Forexample, the amount of fuel injected by the DI fuel injectors may beincreased in order to quickly purge the DI system of ethanol.Cooperatively, the amount of fuel injected via the PI fuel injectors maybe reduced as the amount of fuel injected via the DI fuel injectors isincreased in order to maintain a desired air/fuel ratio. In someexamples, the desired air/fuel ratio may include stoichiometric air/fuelratio. In one particular example, where gasoline and ethanol may beselectively supplied to the DI system, the method may increase thedesired gasoline fraction (GF) during a tip-out, until the DI system ispurged of ethanol. Note that at low engine loads, gasoline may beinjected by only the DI fuel injectors, only the PI fuel injectors, orboth the direct injection fuel injector and the PI fuel injectors.

By supplying ethanol to the DI system at tip-in and supplying gasolineto the DI system at tip-out, ethanol may be directly injected to abateengine knock at high load conditions and gasoline may be directlyinjected to improve exhaust system warm-up at cold start conditions. Inthis way, increased engine output at high load may be provided andtailpipe emissions at engine start may be reduced.

Furthermore, it will be appreciated that by changing fuel supplied tothe DI system at each tip-in and tip-out, the DI system may be suitablypurged during vehicle operation and no additional engine run time isnecessary in order to purge the DI system at key-off. In this way, fueleconomy performance of the vehicle may be improved.

Note that, in the above described flowchart, the use of gasoline andethanol are merely nonlimiting examples of a first fuel type and secondfuel type. Further, note that various other fuels or blends of fuels maybe used in an engine system according to the above described flowchart.The different fuels or fuel blends may have different heats ofvaporization which may dictate when and how they are used during engineoperation.

FIG. 4 shows a flowchart depicting another example fuel control strategyfor improved exhaust system warm-up at vehicle startup and improvedefficiency of engine operation across the operating range of the engine.Like the method described in FIG. 3, this example method may be appliedto different engine configurations that include cylinders having DI fuelinjectors, such as the engine system configuration shown in FIGS. 1 and2. In this example, the engine system may be configured to inject afirst type of fuel (e.g. gasoline) from a first fuel storage tank via PIfuel injectors and at least some of either the first type of fuel (e.g.gasoline) or a second type of fuel (e.g. ethanol) from a second fuelstorage tank may be supplied to DI fuel injectors for direct injectioninto cylinders of the engine. In this strategy the DI system may befilled with ethanol during vehicle operation after warm-up of theexhaust system and the DI system may be purged and filled with gasolineat shutdown, in preparation for a possible ensuing cold start condition.

The flowchart begins at 402, where the method may include detecting akey-on condition. In other words, the method may include detecting adriver commanded vehicle/engine startup. If the key-on condition is notdetected the flowchart may return to 402 and continue polling for thekey-on condition. Otherwise, if the key-on condition is detected theflowchart moves to 404.

At vehicle startup, the temperature of emissions control device(s) inthe vehicle's exhaust system may be below an operating or light-offtemperature. Thus, it may be desirable to heat the emissions controldevice(s) in a quick manner in order to reduce tailpipe emissions.Therefore, at 404, the method may include performing stratified fuelinjections of gasoline via the DI fuel injectors.

Next at 406, the method may include determining if the temperature ofthe emissions control device(s) (ECD) is greater than a thresholdlight-off temperature. If it is determined that the emissions controldevice(s) has/have reached the threshold light-off temperature, theflowchart moves to 410. Otherwise, if it is determined that theemissions control device(s) has/have not reached the threshold light-offtemperature, the flowchart moves to 408 where the method may includedetermining if a key-off condition has occurred. In other words, isvehicle, and more particularly, engine shutdown desired. If the key-offcondition is not detected the method returns to 404 and stratifiedinjections of gasoline may be performed to continue warm-up of theemissions control device(s). Otherwise, if the key-off condition isdetected the flowchart returns and the engine is shutdown without anypurging of the DI fuel system.

Turning to 410, the method may include supplying ethanol from the secondfuel storage tank to the DI fuel injectors in response to the emissionscontrol device(s) reaching a light-off temperature. In an alternativeembodiment, the first fuel may be delivered to the cylinder's directinjector until the cylinder temperature reaches a predetermined level.In one example, the predetermined level is such that ethanol vaporizeswell enough to achieve a desired combustion stability level.

Furthermore, in some embodiments, upon reaching a cylinder temperatureat which ethanol may be stably combusted, the DI fuel injector maytransition from using gasoline from the first fuel storage tank toinjecting stratified ethanol from the second fuel storage tank byincreasing the ethanol fraction (EF).

It will be appreciated that supplying fuel (e.g. ethanol or gasoline) tothe DI fuel injectors may include actuation of one or more valves in thefuel supply control device of the fuel system to stop the flow of thefirst fuel type and start the flow of the second fuel type. In someembodiments, the fuel supply control device may include separate supplylines with separate valves to the DI system and each of the valves maybe actuated to supply the appropriate fuel type to the DI system. Insome embodiments, a single valve may selectively control which fuel typeis supplied to the DI system.

In some embodiments, ethanol may be supplied to the DI system duringlight load conditions, in which case, arbitration may be used todetermine the ratio of gasoline to ethanol in the DI system so that fuelinjection amounts may be adjusted based on the arbitrated ratio in orderto generate a desired air/fuel ratio. In one example, the arbitrationmay consider engine load, air/fuel ratio, time since fuel supply valveactuation, fuel injection mode, etc. To transition between fuel typesquickly, the amount of fuel injected via the DI fuel injectors may betemporarily increased.

In some embodiments, ethanol may be supplied to the DI system inresponse to detection of a first tip-in of the acceleration pedal. Bytransitioning between fuel types at an accelerator tip-in, a transitionbetween fuel types may be performed quickly, and the fuel type beinginjected by the DI fuel injectors may be known with a high accuracyquickly (as opposed to determining a blend of fuel types in the DIsystem).

Next at 412, the method may include adjusting the fuel injection amountinjected by the DI fuel injectors and/or the PI fuel injectors. In oneexample, the DI fuel injectors transition from stratified operation tohomogeneous operation. The DI system may transition from directlyinjecting stratified gasoline and injecting little or no gasoline viaport injection for exhaust warming, to providing port injected gasolinefor primary combustion and selectively injecting ethanol via the DI fuelinjectors at high engine load conditions for knock abatement purposes.Thus, in one example, adjusting the fuel injection amount injected bythe DI fuel injectors and/or the PI fuel injectors may include reducingthe amount of fuel injected by the DI fuel injectors and increasing theamount of fuel injected by the PI fuel injectors. Under some conditions(e.g., low load), fuel may be injected by only the PI fuel injectors.Further, the fuel injection amount may be adjusted to meet a desiredair/fuel ratio, such as a stoichiometric air/fuel ratio, for example.

In this example method, the DI system may be supplied with ethanol fromthe second fuel storage tank during vehicle operation after warm-up ofthe exhaust system (or warm-up of the cylinder). Further, in preparationfor a cold restart condition, ethanol may be purged from the DI systemand gasoline from the first fuel storage tank may be supplied to the DIsystem at shutdown of the vehicle. Thus, at 414, the method may includedetermining if a key-off condition has occurred. In other words, isvehicle, and more particularly, engine shutdown desired. If the key-offcondition is not detected the method may continue polling for thekey-off condition. Otherwise, if the key-off condition is detected theflowchart moves to 416.

At 416, the method may include supplying gasoline from the first fuelstorage tank to the DI fuel injectors. Gasoline may be supplied to theDI system at engine shutdown in preparation for an ensuing cold startcondition.

Next at 418, the method may include purging the DI system of ethanol. Insome embodiments, purging the DI system may include stopping the supplyof ethanol from the second fuel storage tank to the DI system andperforming direct injection of ethanol for combustion after key-off inorder to combust the remaining ethanol in the DI system. Engine designand operation may be modified/adjusted in order to reduce purge timeafter shutdown. In some examples, the DI system may be designed to holda relatively small fuel volume so that purge time may be reduced.Further, in some examples, the engine may be adjusted for inefficientoperation during shutdown. For example, spark timing may be retardedand/or the engine speed may be increased and/or actions may be performedto combust the remaining ethanol at an increased rate so that purge timemay be reduced.

In some embodiments, purging the DI system may include diverting ethanolin the DI system to at least one of the first and second fuel storagetank. In one example, a fuel return line having a control valve mayconnect the DI system with the first tank or the second tank and thecontrol valve may be actuated upon key-off to purge the DI system. Thepurge valve may be opened for a predetermined duration to purge theethanol before being closed. In a particular example, the return line isconnected to the first fuel storage tank containing gasoline, andethanol is purged to the first fuel storage tank since many types ofgasoline contain a blend of ethanol and gasoline. This control strategyavoids the cost of additional return lines to return purged fuel to thefuel storage tank(s).

In another example, the DI system may be connected with the first fuelstorage tank via a first return line and the DI system may be connectedwith the second fuel storage tank via a second return line. Thus, duringpurging, the second fuel line may be used to purge ethanol from the DIsystem and when it is determined that most of the ethanol has beenpurged out, the second return line may be closed and the first returnline may be opened so that the remaining blend of ethanol and gasolinemay be purged to the first tank containing gasoline. This controlstrategy avoids additional run time and fuel consumption after key-off.By only purging ethanol upon engine shutdown, the risk of engine knockduring each tip-in may be avoided since ethanol remains in the DI systemduring vehicle operation. In this way, engine knock may be abated acrossthe range of operating conditions of the vehicle and emissions controldevice(s) may be heated quickly at a cold start condition.

Note that, in the above described flowchart, the use of gasoline andethanol are merely nonlimiting examples of a first fuel type and secondfuel type. Further, note that various other fuels or blends of fuels maybe used in an engine system according to the above described flowchart.The different fuels or fuel blends may have different heats ofvaporization which may dictate when and how they are used at engine coldstart.

The methods described above with reference to FIGS. 3 and 4 facilitatean engine which uses both ethanol and gasoline to achieve improvedoperating efficiency and emissions performance across the operatingrange of the engine. In particular, during cold start and warm-up, themethods make use of mild stratification with gasoline direct injectionfor enhanced fuel evaporation/mixing, combustion stability, andincreased exhaust heat to warm up the catalyst. Further, at light loads,the methods make use of port injected gasoline for minimum ethanolconsumption and good air-fuel mixing. Further still, at high loads, themethods make use of port injected gasoline and directly injected ethanolfor improved knock control with minimum ethanol consumption andincreased engine output.

FIG. 5 shows a flowchart depicting an example fuel control strategy forincreasing the robustness of DI fuel injectors in an engineconfiguration that is capable of supplying fuel from different fuelstorage tanks to the DI fuel injectors. In particular, the method mayreduce or prevent degradation of the DI fuel injectors as a result ofoverheating by supplying fuel to the DI fuel injectors and injectingfuel via the DI fuel injectors even when a fuel storage tank supplyingfuel to the DI fuel injectors is low or substantially empty.

This example method may be applied to different engine configurationsthat include fuel from different sources being supplied to the same ordifferent fuel injectors, such as the engine system configuration shownin FIGS. 1 and 2. In the engine system, a first type of fuel (e.g.gasoline) from a first fuel storage tank may be supplied to the PI fuelinjectors for port injection into cylinders of the engine and at leastsome of either the first type of fuel (e.g. gasoline) from the firsttank or a second type of fuel (e.g. ethanol) from a second fuel storagetank may be supplied to DI fuel injectors for direct injection intocylinders of the engine.

The flowchart begins at 502, where the method may include assessingoperating conditions of the engine system, including current, past,and/or predicted future operating conditions. As described herein,operating conditions may include, but are not limited to, one or more ofthe following: a fuel amount of the first fuel storage tank, a fuelamount of the second fuel storage tank, valve orientation of a directinjection fuel supply passage valve, engine indication of fuel suppliedto the port injection fuel injector, indication of fuel supplied to thedirect injection fuel injector, indication that either of the first orsecond fuel storage tanks has been mis-fueled, engine speed, engineload, combustion mode, air/fuel ratio, ambient conditions such as airtemperature and pressure, spark timing, and vehicle speed, among otheroperating states of the engine system. In a particular example, a secondfuel storage tank primarily supplies fuel to the DI fuel injectors, andthus, assessing operating conditions may include receiving a currentamount of fuel in the second fuel storage tank.

Next at 504, the method may include determining if the amount of fuel inthe second fuel storage tank that is supplying fuel to the DI fuelinjectors exceeds a threshold amount. For example, the threshold amountmay be substantially no fuel in the second fuel storage tank. If it isdetermined that the amount of fuel in the second fuel storage tankexceeds the threshold amount the flowchart moves to 506. Otherwise, theamount of fuel in the second fuel storage tank does not exceed thethreshold amount and the flowchart moves to 508.

At 506, the method may include injecting fuel from the first fuelstorage tank via port injection and/or injecting fuel from the secondfuel storage tank via direct injection based on the current combustionmode. As one example, at low engine load, the PI fuel injectors injectgasoline for combustion and the DI fuel injectors do not perform fuelinjections in order to conserve ethanol. As another example, at highengine load, the PI fuel injectors inject gasoline for combustion andthe DI fuel injectors inject ethanol for engine knock abatement and/orfor cooling of the DI fuel injectors. As yet another example, the DIfuel injectors inject gasoline for combustion, such as for example atvehicle startup.

At 508, the method may include supplying fuel from the first fuelstorage tank to the DI fuel injectors. Fuel may be supplied from thefirst fuel storage tank to the DI fuel injectors in order to reduce orprevent overheating of the DI fuel injectors. Supplying fuel from thefirst fuel storage tank may include actuating one or more valves thatroute fuel from the first fuel storage tank to the direct injection fuelsystem. Further, supplying fuel from the first fuel storage tank mayinclude actuating one or more valves to prevent fuel that may betransferred into the second fuel storage tank from flowing to the DIfuel injectors. In some embodiments, a single valve may be actuated toroute fuel from the first tank and prevent fuel from the second tankbeing supplied to the DI fuel injectors.

Furthermore, supplying fuel from the first fuel storage tank to the DIfuel injectors may result in switching fuel types. For example, thefirst fuel storage tank may be filled with gasoline and the second fuelstorage tank may be filled with ethanol. Thus, when it is determinedthat there is little or no ethanol in the second fuel storage tank theDI fuel injectors may be supplied with gasoline. Further, when it isdetermined that there is little or no gasoline in the first fuel storagetank the DI fuel injectors may be supplied with ethanol from the secondfuel storage tank.

At 510, the method may include adjusting a mode of combustion. The modeof combustion may be adjusted based on the type of fuel supplied to theDI fuel injectors. In particular, if switching between fuel storagetanks results in a change in fuel type being supplied to the DI fuelinjectors, the combustion mode may be adjusted to compensate for thechange in fuel type.

Adjusting the combustion mode may include adjusting the fuel injectionamount of the DI fuel injectors and/or the fuel injection amount of thePI fuel injectors based on the type of fuel being supplied to the DIsystem. Further, adjusting the combustion mode may include adjusting thefuel injection timing of the DI fuel injectors and/or the PI fuelinjectors based on the type of fuel supplied to the DI system.

In one example, if a tank containing ethanol is low or runs out andgasoline is supplied to the direct injection system, under someconditions, the combustion mode may be adjusted to perform directinjection of gasoline, as opposed to port injection of gasoline. Inparticular, at low engine loads, the DI fuel injectors may performstratified injections of gasoline. Thus, the amount of gasoline injectedby the DI fuel injectors may be reduced and the fuel injecting timingmay be retarded (e.g., during compression). Correspondingly, the PI fuelinjectors do not inject gasoline. Further, at moderate engine loads, thefuel injection amount may be adjusted for stoichiometry and the fuelinjection timing may be adjusted to inject fuel during an intake strokefor homogenous combustion. Further still, at high engine loads, the fuelinjection amount may be adjusted to operate slightly rich and the fuelinjection timing maybe adjusted to inject fuel during an intake strokefor homogenous combustion. By adjusting the combustion mode to directlyinject gasoline fuel efficiency and emissions control of the engine maybe improved during some operating conditions.

Note that at moderate and high engine loads, fuel injection may beperformed via direct injection and/or port injection.

In another example, if a tank containing gasoline is low or runs out andethanol is supplied to the direct injection system, the combustion modemay be adjusted to perform direct injection of ethanol. Fuel injectionamount and timing may be adjusted to operate lean, at stoichiometry, orslightly rich based on engine load.

Adjusting the combustion mode may include temporarily deactivating aparticular combustion mode based on the fuel type used in the combustionmode. For example, if ethanol runs out, a combustion mode where ethanolis directly injected and gasoline is port injected may be deactivated,and a high turbocharger boost mode may also be deactivated. As anotherexample, if gasoline runs out, a combustion mode where stratified directinjection of gasoline is performed may be deactivated.

Furthermore, a combustion mode may be reactivated in response to thefuel storage tank being filled with an amount of fuel that is beyond thethreshold amount.

It will be appreciated that references to fuel storage tanks discussedabove may also apply to different outlets of a fuel separation device.For example, a first type of fuel stored in a first fuel storage tankand a second type of fuel stored in a second fuel storage tank maycorrespond to a first type of fuel flowing from a first outlet of a fuelseparation device and a second type of fuel flowing from a second outletof the fuel separation device.

Note the above described method is one nonlimiting example ofselectively supplying different types of fuel from different sources tothe direct injection fuel injector and/or the port injection fuelinjector according to different operating conditions. Moreover, it willbe appreciated that different types of fuel from different sources maybe selectively supplied to the direct injection fuel injector and/or theport injection fuel injector according to various different operatingconditions.

For example, a vehicle system may be configured such that a PI fuelinjector may be supplied with fuel from at least one of a first fuelstorage tank and a second fuel storage tank and a DI fuel injector maybe selectively supplied with fuel from one of the first fuel storagetank and the second fuel storage tank. In one example, where the PI fuelinjector is supplied with the first type of fuel from the first fuelstorage tank and the DI fuel injector is supplied with the second typeof fuel from the second fuel storage tank, the DI fuel injector may notreceive fuel based a disruption in the fuel supply system (e.g., ablocked fuel supply valve or supply line). The disruption may bedetected in various manners. For example, a sensor positioned proximateto the DI fuel injector (e.g., at the DI fuel rail or high pressure fuelpump) may detect that no fuel is being supplied from the second fuelstorage tank, and thus the DI fuel injector may be supplied with fuelfrom the first fuel storage tank. As another example, the disruption inthe fuel supply system may be detected based on a variation in air/fuelratio as a result of less fuel being supplied and/or injected by the DIfuel injector, and thus the DI fuel injector may be supplied with fuelfrom the first fuel storage tank.

In another example, where the PI fuel injector is supplied with thefirst type of fuel from the first fuel storage tank and the DI fuelinjector is supplied with the second type of fuel from the second fuelstorage tank, the second fuel storage tank may be mis-fueled (e.g.,filled with an unexpected type of fuel, contaminated, etc.). Themis-fuel may be detected in various manners. For example, a sensor inthe second fuel tank may detect a type of fuel supplied to the tank. Asanother example, the indication of a mis-fuel may be supplied by avehicle operator or service provider via an input. As yet anotherexample, the mis-fuel may be detected based on changes in operatingparameters such as engine output, emissions, air/fuel ratio, etc. Inresponse to receiving an indication of a mis-fuel, the DI fuel injectormay be supplied with the second type of fuel from the second fuelstorage tank. By supplying at least some fuel to the DI fuel injectorfrom a different source based on an indication that fuel is beingsupplied to DI fuel injector, fuel may be supplied to the DI fuelinjector at various conditions to cool the DI fuel injector. In thisway, overheating of the DI fuel injector may be reduced.

Note that the example control and estimation routines included hereincan be used with various system configurations. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations, orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the features and advantages of theexample embodiments described herein, but is provided for ease ofillustration and description. One or more of the illustrated actions,functions, or operations may be repeatedly performed depending on theparticular strategy being used. Further, the described operations,functions, and/or acts may graphically represent code to be programmedinto computer readable storage medium in the control system.

It will be appreciated that the configurations disclosed herein areexemplary in nature, and that these specific embodiments are not to beconsidered in a limiting sense, because numerous variations arepossible. The subject matter of the present disclosure includes allnovel and nonobvious combinations and subcombinations of the varioussystems and configurations, and other features, functions, and/orproperties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A vehicle system comprising: a fuel system containing a first type offuel and a second type of fuel at least one cylinder; a port injectionfuel injector to inject fuel into an intake passage in operativecommunication with the at least one cylinder, the port injection fuelinjector being supplied with a first type of fuel from the fuel system;a direct injection fuel injector to inject fuel directly into the atleast one cylinder, the direct injection fuel injector being selectivelysupplied with at least one of the first type of fuel and the second typeof fuel from the fuel system; an emissions control device positioned toreceive emissions exhausted from the at least one cylinder; and acontrol system configured to cause the first type of fuel from the fuelsystem to be supplied to the direct injection fuel injector in responseto an engine start condition, to cause the second type of fuel to besupplied from the fuel system to the direct injection fuel injectorbased on a temperature of the emissions control device exceeding athreshold temperature, and to cause the second type of fuel to besupplied from the fuel system to the direct injection fuel injectorbased on an increased in engine output even when the temperature isbelow the threshold temperature.
 2. The system of claim 1, wherein thefuel system comprises: a first fuel storage tank to store the first typeof fuel, the first fuel storage tank in fluid communication with theport injection fuel injector and selective fluid communication with thedirect injection fuel injector; and a second fuel storage tank to storethe second type of fuel, the second fuel storage tank in selective fluidcommunication with the direct injection fuel injector.
 3. The system ofclaim 1, wherein the fuel system comprises: a first fuel supply passagein communication with the port injection fuel injector and in selectivefluid communication with the direct injection fuel injector; a secondfuel supply passage in selective fluid communication with the directinjection fuel injector; and a fuel separator configured to receive afuel blend and separate the first type of fuel into the first fuelsupply passage and the second type of fuel to the second fuel supplypassage from the fuel blend.
 4. A vehicle system, comprising: a firstfuel storage tank; a second fuel storage tank; at least one cylinder; aport injection fuel injector to inject fuel into an intake passage inoperative communication with the at least one cylinder, the portinjection fuel injector being supplied with a first type of fuel fromthe first fuel storage tank; a direct injection fuel injector to injectfuel directly into the at least one cylinder, the direct injection fuelinjector being selectively supplied with the first type of fuel from thefirst fuel storage tank and a second type of fuel from the second fuelstorage tank; an emissions control device positioned to receiveemissions exhausted from the at least one cylinder; and a control systemconfigured to cause the first type of fuel from the first fuel storagetank to be supplied to the direct injection fuel injector in response toan engine start condition, said control system further configured tosupply the second type of fuel from the second fuel storage tank basedon a temperature of the emissions control device exceeding a thresholdtemperature, and configured to cause the direct injection fuel injectorto be purged of fuel for a predetermined duration in response to anoperating condition.
 5. The system of claim 4, wherein the operatingcondition includes at least one of a change in position of an operatorpedal position exceeding a threshold change and an engine shut-offcondition.
 6. The system of claim 4, further comprising: a fuelseparator in operative communication with the first fuel storage tankand the second fuel storage tank, the fuel separator configured toseparate a fuel blend including the first type of fuel and the secondtype of fuel, such that the first type of fuel is supplied to the firstfuel storage tank and the second type of fuel is supplied to the secondfuel storage tank.
 7. The system of claim 6, wherein fuel purged fromthe direct injection fuel injector is supplied to the fuel separator. 8.The system of claim 4, wherein during purging of fuel from the directinjection fuel injector, the amount of fuel injected by the directinjection fuel injector is increased for the predetermined duration andthe fuel is purged via combustion.
 9. The system of claim 4, furthercomprising: a fuel supply control device having at least one valveconfigured to regulate supply of at least one of the first type of fuelfrom the first fuel storage tank and the second type of fuel from thesecond fuel storage tank, and the control system is configured to causeactuation of the at least one valve of the fuel supply control device tocontrol supply of the fuel to the direct injection fuel injector.
 10. Amethod of controlling fuel supplied to an engine of a vehicle, thevehicle including a first fuel storage tank to store a first type offuel, a second fuel storage tank to store a second type of fuel, and anemissions control device, the engine including at least one cylinderhaving a direct injection fuel injector being selectively supplied withthe first type of fuel from the first fuel storage tank and the secondtype of fuel from the second fuel storage tank, the method comprising:supplying the first type of fuel from the first fuel storage tank to atleast a direct injection fuel injector in response an engine startcondition of the vehicle; and supplying the second type of fuel from thesecond fuel storage tank to said at least a direct injection fuelinjector, in response to an increase in engine output exceeding athreshold increase or a temperature of the emissions control deviceexceeding a threshold temperature.
 11. The method of claim 10, whereinthe second type of fuel from the second fuel storage tank is notsupplied to said at least a direct injection fuel injector when thefirst type of fuel from the first fuel storage tank is being supplied tosaid at least direct injection fuel injector and the first type of fuelfrom the first fuel storage tank is not supplied to said at least directinjection fuel injector when the second type of fuel from the secondfuel storage tank is being supplied to said at least direct injectionfuel injector.
 12. The method of claim 10, further comprising:performing stratified injections using the first type of fuel via thedirect injection fuel injector in response to the temperature of theemissions control device not exceeding the threshold temperature. 13.The method of claim 10, further comprising: supplying the first type offuel from the first fuel storage tank to the direct injection fuelinjector, at a commanded decrease in engine output that exceeds athreshold decrease and that occurs after the commanded increase inengine output.
 14. The method of claim 13, further comprising:increasing a fuel injection amount of the direct injection fuel injectorfor a predetermined duration following the commanded decrease in engineoutput.
 15. The method of claim 10, further comprising: supplying thefirst type of fuel from the first fuel storage tank to the directinjection fuel injector in response to an engine shut-off condition. 16.The method of claim 15, further comprising: performing combustion of airand fuel injected via the direct injection fuel injector for apredetermined duration in response to the engine shut-off condition. 17.The method of claim 15, further comprising: purging fuel from the directinjection fuel injector to at least one of the first fuel storage tankand the second fuel storage tank for a predetermined duration in respondto the engine shut-off condition.
 18. The method of claim 10, whereinthe threshold temperature is the light-off temperature of the emissionscontrol device.
 19. The method of claim 10, wherein the thresholdincrease and the threshold decrease is based on a position of anoperator input pedal of the vehicle.
 20. The method of claim 10, whereinthe engine further includes a port injection fuel injector beingsupplied with the first type of fuel from the first fuel storage tank,the method further comprising: in response to the temperature of theemissions control device exceeding the threshold temperature, performingfuel injection via the port injection fuel injector at low loadcondition.